I. Field of the Invention
This invention relates generally to catheters for facilitating the performance of transluminal valvuloplasty, and more particularly to the construction of such a catheter whereby the balloon or expander member is stabilized during the inflation thereof to inhibit movement of the balloon beyond the location of the valve being treated.
II. Discussion of the Prior Art
Between each atrium and ventricle of the heart, there is a somewhat constricted opening referred to as the atrioventricular orifice which is strengthened by fibrous rings and protected by valves. Also, the openings into the aorta and the pulmonary artery are also guarded by valves. More particularly, the orifice between the right ventricle and the pulmonary artery is guarded by the pulmonary valve and the orifice between the left ventricle and the aorta is guarded by the aortic valve. These two valves are called "semilunar valves" and consist of three semilunar cusps, each cusp being attached by its convex margin to the inside of the artery where it joins the ventricle, while its free border projects into the lumen of the vessel.
In the healthy heart, the semilunar valves offer no resistance to the passage of blood from the heart into the arteries as the free borders of the valve project into the arteries, but they form a complete barrier to the passage of blood in the opposite direction. In this case, each pocket becomes filled with blood, and the free borders are floated out and distended so that they meet in the center of the vessel. With age, however, the commissure lines defining the interface between the cusps can become calcified, inhibiting the ability of the valve to open and close in a normal fashion. In the past, such problems have been surgically addressed by opening the heart and repairing or replacing the valve with a man-made or animal replacement valve.
A more recent medical advance in the treatment of calcified coronary valves has involved the so-called transluminal valvuloplasty procedure in which, for example, in treating the aortic valve, a catheter is introduced into the femoral artery and advanced upward through the vascular system until it passes through the aorta to the site of the aortic semilunar valve. The catheter is equipped with a "balloon" near its distal end which is capable of being inflated to a predetermined maximum diameter by the introduction of an inflation fluid at the proximal end of the catheter structure. Expansion of the balloon while in the location of the valve is found to fracture the calcification, opening the commissure lines and again allowing the cusps to appropriately flex.
In some instances, it has been difficult to maintain the balloon at the desired position during the inflation thereof. Blood is inherently a slippery medium and as the inflation fluid is introduced into the balloon and it begins to swell, there is a tendency for the balloon to pop out of the valve site and, in some instances, it has been known to be projected with a sufficient force into the ventricle to perforate the ventricle near its apex, resulting in death.
In the Inoue U.S. Pat. No. 4,327,736, there is disclosed a balloon catheter especially designed for expanding a hollow organ and restoring resiliency to a theretofore stenosed structure. In accordance with the invention described therein, the balloon incorporates a non-extendable bag structure for defining the outer limit to which the balloon may be expanded. Surrounding the balloon are one or more elastic bands. When an inflation fluid is injected into the interior of the balloon to cause it to expand, the rubber bands cause the balloon to expand so as to create a dog-bone shape which tends to stabilize the balloon within the constriction being treated as expansion takes place.